Validate Windows support

[sudomateo]

There's no technical reason that this plugin shouldn't support Windows, but during initial development only Linux images were tested. Ensure this plugin works with Windows images and, notably, the winrm communicator.

[linear]

SSE-155

[sudomateo]

This plugin successfully works with Windows. In fact, I'm migrating Oxide's Windows image builder to Packer in oxidecomputer/windows-image-builder#30. Closing this.